This term has inconsistently been used to mean cyclohepta-1,3,5-trienes or to mean
cyclohepta-1,3,5-trienes in dynamic equilibrium with bicyclo-[4.1.0]hepta-2,4-
dienes, so that the structure of the bulk substance is indeterminate in the time scale of
the method of observation. Use of this term is therefore discouraged.
Source:
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1373